// SPDX-License-Identifier: GPL-2.0
/*
 * arch/sh/kernel/cpu/sh5/unwind.c
 *
 * Copyright (C) 2004  Paul Mundt
 * Copyright (C) 2004  Richard Curnow
 */
#include <linux/kallsyms.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/errno.h>
#include <asm/page.h>
#include <asm/ptrace.h>
#include <asm/processor.h>
#include <asm/io.h>
#include <asm/unwinder.h>
#include <asm/stacktrace.h>

static u8 regcache[63];

/*
 * Finding the previous stack frame isn't horribly straightforward as it is
 * on some other platforms. In the sh64 case, we don't have "linked" stack
 * frames, so we need to do a bit of work to determine the previous frame,
 * and in turn, the previous r14/r18 pair.
 *
 * There are generally a few cases which determine where we can find out
 * the r14/r18 values. In the general case, this can be determined by poking
 * around the prologue of the symbol PC is in (note that we absolutely must
 * have frame pointer support as well as the kernel symbol table mapped,
 * otherwise we can't even get this far).
 *
 * In other cases, such as the interrupt/exception path, we can poke around
 * the sp/fp.
 *
 * Notably, this entire approach is somewhat error prone, and in the event
 * that the previous frame cannot be determined, that's all we can do.
 * Either way, this still leaves us with a more correct backtrace then what
 * we would be able to come up with by walking the stack (which is garbage
 * for anything beyond the first frame).
 *                                              -- PFM.
 */
static int lookup_prev_stack_frame(unsigned long fp, unsigned long pc,
                      unsigned long *pprev_fp, unsigned long *pprev_pc,
                      struct pt_regs *regs)
{
        const char *sym;
        char namebuf[128];
        unsigned long offset;
        unsigned long prologue = 0;
        unsigned long fp_displacement = 0;
        unsigned long fp_prev = 0;
        unsigned long offset_r14 = 0, offset_r18 = 0;
        int i, found_prologue_end = 0;

        sym = kallsyms_lookup(pc, NULL, &offset, NULL, namebuf);
        if (!sym)
                return -EINVAL;

        prologue = pc - offset;
        if (!prologue)
                return -EINVAL;

        /* Validate fp, to avoid risk of dereferencing a bad pointer later.
           Assume 128Mb since that's the amount of RAM on a Cayman.  Modify
           when there is an SH-5 board with more. */
        if ((fp < (unsigned long) phys_to_virt(__MEMORY_START)) ||
            (fp >= (unsigned long)(phys_to_virt(__MEMORY_START)) + 128*1024*1024) ||
            ((fp & 7) != 0)) {
                return -EINVAL;
        }

        /*
         * Depth to walk, depth is completely arbitrary.
         */
        for (i = 0; i < 100; i++, prologue += sizeof(unsigned long)) {
                unsigned long op;
                u8 major, minor;
                u8 src, dest, disp;

                op = *(unsigned long *)prologue;

                major = (op >> 26) & 0x3f;
                src   = (op >> 20) & 0x3f;
                minor = (op >> 16) & 0xf;
                disp  = (op >> 10) & 0x3f;
                dest  = (op >>  4) & 0x3f;

                /*
                 * Stack frame creation happens in a number of ways.. in the
                 * general case when the stack frame is less than 511 bytes,
                 * it's generally created by an addi or addi.l:
                 *
                 *      addi/addi.l r15, -FRAME_SIZE, r15
                 *
                 * in the event that the frame size is bigger than this, it's
                 * typically created using a movi/sub pair as follows:
                 *
                 *      movi    FRAME_SIZE, rX
                 *      sub     r15, rX, r15
                 */

                switch (major) {
                case (0x00 >> 2):
                        switch (minor) {
                        case 0x8: /* add.l */
                        case 0x9: /* add */
                                /* Look for r15, r63, r14 */
                                if (src == 15 && disp == 63 && dest == 14)
                                        found_prologue_end = 1;

                                break;
                        case 0xa: /* sub.l */
                        case 0xb: /* sub */
                                if (src != 15 || dest != 15)
                                        continue;

                                fp_displacement -= regcache[disp];
                                fp_prev = fp - fp_displacement;
                                break;
                        }
                        break;
                case (0xa8 >> 2): /* st.l */
                        if (src != 15)
                                continue;

                        switch (dest) {
                        case 14:
                                if (offset_r14 || fp_displacement == 0)
                                        continue;

                                offset_r14 = (u64)(((((s64)op >> 10) & 0x3ff) << 54) >> 54);
                                offset_r14 *= sizeof(unsigned long);
                                offset_r14 += fp_displacement;
                                break;
                        case 18:
                                if (offset_r18 || fp_displacement == 0)
                                        continue;

                                offset_r18 = (u64)(((((s64)op >> 10) & 0x3ff) << 54) >> 54);
                                offset_r18 *= sizeof(unsigned long);
                                offset_r18 += fp_displacement;
                                break;
                        }

                        break;
                case (0xcc >> 2): /* movi */
                        if (dest >= 63) {
                                printk(KERN_NOTICE "%s: Invalid dest reg %d "
                                       "specified in movi handler. Failed "
                                       "opcode was 0x%lx: ", __func__,
                                       dest, op);

                                continue;
                        }

                        /* Sign extend */
                        regcache[dest] =
                                sign_extend64((((u64)op >> 10) & 0xffff), 9);
                        break;
                case (0xd0 >> 2): /* addi */
                case (0xd4 >> 2): /* addi.l */
                        /* Look for r15, -FRAME_SIZE, r15 */
                        if (src != 15 || dest != 15)
                                continue;

                        /* Sign extended frame size.. */
                        fp_displacement +=
                                (u64)(((((s64)op >> 10) & 0x3ff) << 54) >> 54);
                        fp_prev = fp - fp_displacement;
                        break;
                }

                if (found_prologue_end && offset_r14 && (offset_r18 || *pprev_pc) && fp_prev)
                        break;
        }

        if (offset_r14 == 0 || fp_prev == 0) {
                if (!offset_r14)
                        pr_debug("Unable to find r14 offset\n");
                if (!fp_prev)
                        pr_debug("Unable to find previous fp\n");

                return -EINVAL;
        }

        /* For innermost leaf function, there might not be a offset_r18 */
        if (!*pprev_pc && (offset_r18 == 0))
                return -EINVAL;

        *pprev_fp = *(unsigned long *)(fp_prev + offset_r14);

        if (offset_r18)
                *pprev_pc = *(unsigned long *)(fp_prev + offset_r18);

        *pprev_pc &= ~1;

        return 0;
}

/*
 * Don't put this on the stack since we'll want to call in to
 * sh64_unwinder_dump() when we're close to underflowing the stack
 * anyway.
 */
static struct pt_regs here_regs;

extern const char syscall_ret;
extern const char ret_from_syscall;
extern const char ret_from_exception;
extern const char ret_from_irq;

static void sh64_unwind_inner(const struct stacktrace_ops *ops,
                              void *data, struct pt_regs *regs);

static inline void unwind_nested(const struct stacktrace_ops *ops, void *data,
                                 unsigned long pc, unsigned long fp)
{
        if ((fp >= __MEMORY_START) &&
            ((fp & 7) == 0))
                sh64_unwind_inner(ops, data, (struct pt_regs *)fp);
}

static void sh64_unwind_inner(const struct stacktrace_ops *ops,
                              void *data, struct pt_regs *regs)
{
        unsigned long pc, fp;
        int ofs = 0;
        int first_pass;

        pc = regs->pc & ~1;
        fp = regs->regs[14];

        first_pass = 1;
        for (;;) {
                int cond;
                unsigned long next_fp, next_pc;

                if (pc == ((unsigned long)&syscall_ret & ~1)) {
                        printk("SYSCALL\n");
                        unwind_nested(ops, data, pc, fp);
                        return;
                }

                if (pc == ((unsigned long)&ret_from_syscall & ~1)) {
                        printk("SYSCALL (PREEMPTED)\n");
                        unwind_nested(ops, data, pc, fp);
                        return;
                }

                /* In this case, the PC is discovered by lookup_prev_stack_frame but
                   it has 4 taken off it to look like the 'caller' */
                if (pc == ((unsigned long)&ret_from_exception & ~1)) {
                        printk("EXCEPTION\n");
                        unwind_nested(ops, data, pc, fp);
                        return;
                }

                if (pc == ((unsigned long)&ret_from_irq & ~1)) {
                        printk("IRQ\n");
                        unwind_nested(ops, data, pc, fp);
                        return;
                }

                cond = ((pc >= __MEMORY_START) && (fp >= __MEMORY_START) &&
                        ((pc & 3) == 0) && ((fp & 7) == 0));

                pc -= ofs;

                ops->address(data, pc, 1);

                if (first_pass) {
                        /* If the innermost frame is a leaf function, it's
                         * possible that r18 is never saved out to the stack.
                         */
                        next_pc = regs->regs[18];
                } else {
                        next_pc = 0;
                }

                if (lookup_prev_stack_frame(fp, pc, &next_fp, &next_pc, regs) == 0) {
                        ofs = sizeof(unsigned long);
                        pc = next_pc & ~1;
                        fp = next_fp;
                } else {
                        printk("Unable to lookup previous stack frame\n");
                        break;
                }
                first_pass = 0;
        }

        printk("\n");
}

static void sh64_unwinder_dump(struct task_struct *task,
                               struct pt_regs *regs,
                               unsigned long *sp,
                               const struct stacktrace_ops *ops,
                               void *data)
{
        if (!regs) {
                /*
                 * Fetch current regs if we have no other saved state to back
                 * trace from.
                 */
                regs = &here_regs;

                __asm__ __volatile__ ("ori r14, 0, %0" : "=r" (regs->regs[14]));
                __asm__ __volatile__ ("ori r15, 0, %0" : "=r" (regs->regs[15]));
                __asm__ __volatile__ ("ori r18, 0, %0" : "=r" (regs->regs[18]));

                __asm__ __volatile__ ("gettr tr0, %0" : "=r" (regs->tregs[0]));
                __asm__ __volatile__ ("gettr tr1, %0" : "=r" (regs->tregs[1]));
                __asm__ __volatile__ ("gettr tr2, %0" : "=r" (regs->tregs[2]));
                __asm__ __volatile__ ("gettr tr3, %0" : "=r" (regs->tregs[3]));
                __asm__ __volatile__ ("gettr tr4, %0" : "=r" (regs->tregs[4]));
                __asm__ __volatile__ ("gettr tr5, %0" : "=r" (regs->tregs[5]));
                __asm__ __volatile__ ("gettr tr6, %0" : "=r" (regs->tregs[6]));
                __asm__ __volatile__ ("gettr tr7, %0" : "=r" (regs->tregs[7]));

                __asm__ __volatile__ (
                        "pta 0f, tr0\n\t"
                        "blink tr0, %0\n\t"
                        "0: nop"
                        : "=r" (regs->pc)
                );
        }

        sh64_unwind_inner(ops, data, regs);
}

static struct unwinder sh64_unwinder = {
        .name   = "sh64-unwinder",
        .dump   = sh64_unwinder_dump,
        .rating = 150,
};

static int __init sh64_unwinder_init(void)
{
        return unwinder_register(&sh64_unwinder);
}
early_initcall(sh64_unwinder_init);